An Etymological Dictionary of the German Language/kostspielig

by Friedrich Kluge

kostspielig, adj., ‘expensive,’ first used towards the end of the 18th cent.; it contains, however, an old word which has elsewhere disappeared, and even in this compound has been corrupted; MidHG. spildec, ‘extravagant’; OHG. spilden, ‘to squander, dissipate’ (from OHG. gaspilden, Fr. gaspiller is derived). Hence *kostspildig is probably ‘squandering money’; spildig, which was etymologically obscure, was corrupted into -spielig.